In cellular mobile communication, when a mobile station apparatus detects that it is situated near an end of a cell, it measures reception quality of signal from a target base station apparatus situated around the serving base station to which it is connected at present. If the measured reception quality of the target base station apparatus satisfies a prescribed reference, the mobile station executes handover for switching the current connection to the target base station apparatus. In the description that follows, a mobile station and a base station are denoted-simply as “MS” and “BS”, respectively.
An asynchronous CDMA (Code Division Multiple Access) mobile communication system has been known in which a plurality of mobile stations measure relative time difference between various BS pairs and these measurements are stored in the BS. In this system, the source BS transmits estimated relative time difference between the source BS and each BS included in a list of adjoining cells to MS. Each BS included in the list can maintain a table of estimated relative time difference, and this table can be continuously updated using measurement report received from MS. Thereafter, BS transmits the entry of this table to MS in an adjoining cell list message. The BS knows the relative timing difference. When the MS starts cell search for a candidate BS, MS can estimate the timing of the candidate BS as compared to the source BS.
It has also been known to set measurement timing shifted by every guard interval length within the range of maximum delay difference before or after the timing of receiving a signal from the serving base station, and to measure reception quality of a target base station at each measurement timing. The measured best reception quality is reported to the serving base station as the reception quality of the target base station.